Using GNU Parallel with ia

GNU Parallel is a shell tool for executing jobs in parallel. It is a very useful tool to use with ia for bulk jobs. It can be installed via many OS package managers.

For example, it can be installed via homebrew on Mac OS:

brew install parallel

Refer to the GNU Parallel homepage for more details on available packaes, source code, installation, and other documentation and tutorials.

Basic Usage

You can use parallel to retrieve metadata from items concurrently:

$ cat itemlist.txt
$ cat itemlist.txt | parallel 'ia metadata {}' | jq

You can run parallel with --dry-run to check your commands before running them:

$ cat itemlist.txt | parallel --dry-run 'ia metadata {}'
ia metadata jj-test-2020-09-17-2
ia metadata jj-test-2020-09-17-1
ia metadata jj-test-2020-09-17-3

Logging and retrying with Parallel

Parallel also offers an easy way to log and retry failed commands.

Here’s an example of a job that is retrieving metadata for all of the items in the file named itemlist.txt, and outputing the metadata to a file named output.jsonl. It uses the --joblog option to log all commands and their exit value to /tmp/my_ia_job.log:

$ cat itemlist.txt | parallel --joblog /tmp/my_ia_job.log 'ia metadata {}' > output.jsonl

You can now retry any commands that failed by using the --retry-failed option (don’t forget to switch > to >> in this example, so you don’t overwrite output.jsonl! >> means to append to the output file, rather than clobber it):

$ parallel --retry-failed --joblog /tmp/my_ia_job.log 'ia metadata {}' >> output.jsonl

If there were no failed commands, nothing will be rerun. You can rerun this command until it exits with 0. You can check the exit code by running echo $? directly after the parallel command finishes.